A joining structure of this type is known and is found in panels whose width exceeds the width in which the metal layers are produced. Examples of panels of this type which may be mentioned include the skin panels of airplanes, for example those being used for the airplane's fuselage. In an application of this kind, the panels also have to be provided with apertures of a particular size. In this context, in addition to the apertures for windows, it is mainly the relatively large apertures, such as those used for doors and hatches and the like, which are relevant.
In theory, such apertures weaken the panel's supporting function. By applying local reinforcements, it is nevertheless possible to maintain the desired mechanical properties of the panel, such as stiffness and strength. Such reinforcements may be in the form of girders and joists, but in many cases the local reinforcements used are in the form of additional layers in the laminate, in the region of the aperture.
These local reinforcing layers are likewise made from sheet material having a particular maximum width and usually consist of the same material as the metal layers in the remainder of the laminate. The sheet material, which is usually supplied in the form of coils, is directionally sensitive with respect to its mechanical properties as a result of the manufacturing procedure. This directional sensitivity is caused, inter alia, by the direction of the rolling treatment to which the material is subjected. The rolling direction results in a grain orientation in the material.
It is desirable to take the grain orientation into account when manufacturing panels from this type of material, in view of the desired mechanical properties of the said panels. In the present case, this means that the reinforcement layers must have the same grain orientation as the metal layers in the laminate. The result of this is that in panels containing joins, the reinforcing layers must also have joins, since they cannot be provided in the longitudinal direction of the strip transverse to the joining structure, as the grain orientation would then be incorrect. These joins in the reinforcement layers are preferably in close proximity to the joins in the laminate itself.